Create missing unit tests on classes added in AppFormer.js

AppFormer.js initiative brought many capabilities to the existing AppFormer implementation, but some of them are still yet to be used. When this happens, we need to make sure that they're well tested.

These are the classes that are still to test:

• AppFormerJsBridge#rpc
• AppFormerJsBridge#goToPath
• AppFormerJsBridge#registerPerspective
• AppFormerJsBridge#registerEditor
• JsWorkbenchPanelConverter
• JsWorkbenchPartConverter
• JsWorkbenchPerspectiveActivity
• JsWorkbenchTemplatedPerspectiveActivity

If more classes and methods to be tested are identified they should be added in this JIRA.